inline function ‘typename Eigen::MatrixBase<Derived>::cross_product_return_type<OtherDerived>::type Eigen::MatrixBase<Derived>::cross(const Eigen::MatrixBase<OtherDerived>&) const [with OtherDerived = Eigen::Matrix<double, 3, 1>; Derived = Eigen::Matrix<double, 3, 1>; typename Eigen::MatrixBase<Derived>::cross_product_return_type<OtherDerived>::type = Eigen::Matrix<double, 3, 1>]’ used but never defined